The library's collection of 300,000 volumes includes audio recordings and periodicals as well as books on a broad range of subjects. It is open for browsing and research by the general public; only members may borrow or use the upper floors. The library is a non-profit organization supported primarily by its membership fees and endowment.

Like other subscription libraries at the time, members paid a membership fee to access the collection. A board of trustees was elected which hired the librarians, chose materials for the collection and drafted and enforced regulations about library use.[6] The nature of the collection represented the ideals of the library and contained works of a great variety. Although Christian theological texts were included, so was the Koran and books on Catholic saints and popes. There were a variety of natural philosophy texts alongside works by Shakespeare. [6] Resources were also available for a variety of vocational purposes, including manuals for merchants and farmers.

By 1856, the collection had reached 35,000 and it was once again time for the library to move. A larger building for its exclusive use was erected at 109 University Place, reflecting the city's continuing northerly expansion. Herman Melville and Willa Cather were among the visitors to that location.[3][4] It had a double-height central reading room and shelf space for 100,000 books.[2] This building would serve the NYSL for 81 years.

In 1937, with the collection having grown to 150,000 volumes, the library moved to its present location at 53 East 79th Street, on the Upper East Side between Madison and Park avenues, with the help of a generous donation that enabled the purchase of the building, a mansion built just 20 years earlier. Notable patrons at the present location have ranged from W. H. Auden and Lillian Hellman in the early years to David Halberstam and Wendy Wasserstein more recently.[3][4]

On the upper stories the stone is laid in an ashlar pattern with quoins at the corners. The second story windows are double glass doors topped with carvedbracketedpediments (rounded in the center). Belt courses at sill level divide the stories. Above the fifth story the roofline is marked by a frieze and cornice topped by another balustrade. Behind it is a small terrace sheltered by a wide overhang. An end chimney rises from the gabled tile roof.[4]

The interior was extensively modified for the library in 1937. Much of this effort was focused on the rear; when it was completed, 39 rooms had been combined into 24. Original treatments remain, such as the coffered ceilings, stone walls and arched entryways on the first and second floors. The wood paneling and mantels in the card catalog room, second floor lounge and director's office is also original.[4]Architectural historianHenry Hope Reed Jr. has described the main stairs as "the only [ones] in New York fit for a cardinal".[2]

Members pay an annual fee of $225 for borrowing privileges and access to the upper floors, with two closed stacks,[7] a members' lounge and exhibit hall.[2] Those fees and the library's endowment support a staff of 16 full-time and 20 part-time employees, supplemented by several volunteers and headed by director Mark Bartlett.[8] The library acquires an average of 4,000 new volumes every year[9] and subscribes to approximately 100 periodicals.[9]

The collection also includes a children's library and 10,000 volumes in its special collections. Foremost among these latter are 290 books from the personal library kept by Puritan settler John Winthrop and his descendants.[10] Another significant collection are the Italian-language books kept by Mozart's librettistLorenzo Da Ponte, who spent his last years in New York. He started an Italian Library Society in 1827 under the New York Society's auspices, to supplement his courses at Columbia, the first college courses in that language in the United States. Those 600 volumes made up a large share of the library's 1838 catalog, and are today separately organized as the Da Ponte collection.[11]

The library also partners with other cultural institutions in the city. It has presented exhibitions in conjunction with the Metropolitan Museum of Art[12] and chamber music performances.[13] In conjunction with WNET television, the local PBS station, it has had four to six Author Series events every year since 1997, in which the writers of recently published nonfiction works (and sometimes, novels), such as Caroline Alexander and Erica Jong, discuss them with an audience.[14]